Unity is more user friendly than Blender, imo. It comes with some great, pre-built assets to get you started, like first or third person controller, tree creator and it has a terrain editor. Building maps is MUCH easier than in Blender, although you do have to build models in other software and import them. It's about 1000x easier to make a HUD also
It's quite different from Blender for handling variables and scripts (which can be in JavaScript, C# or Boo). It took me maybe a week to get used to. I haven't tackled AI yet, but I believe that Blender may have a slight edge since it comes with NavMesh functions--but I'm not sure.
Also, it's supposed to have more efficient physics and graphics, but my games aren't complex enough to notice
